Known dry-cleaning processes consist of wash, rinse, and drying cycles. Garments are loaded into a basket in a cleaning drum and immersed in a dry-cleaning fluid or solvent, which is pumped into the cleaning drum from a base tank. Conventional dry-cleaning fluids include perchloroethylene (PCE), petroleum-based or Stoddard solvents, CFC-113, and 1,1,1-trichloroethane, all of which are generally aided by a detergent. The solvent is used to dissolve soluble contaminants, such as oils, and to entrain and wash away insoluble contaminants, such as dirt.
The use of these conventional solvents, however, poses a number of health and safety risks as well as being environmentally hazardous. For example, halogenated solvents are known to be environmentally unfriendly, and at least one of these solvents, PCE, is a suspected carcinogen. Known petroleum-based solvents are flammable and can contribute to the production of smog. Accordingly, dry-cleaning systems which utilize dense phase fluids, such as liquid carbon dioxide, as a cleaning medium have been developed. An apparatus and method for employing liquid carbon dioxide as the dry-cleaning solvent is disclosed in U.S. Pat. No. 5,467,492, entitled "Dry-Cleaning Garments Using Liquid Carbon Dioxide Under Agitation As Cleaning Medium". A similar dry-cleaning apparatus is also disclosed in U.S. Pat. No. 5,651,276.
These systems pose a number of other problems, particularly in relation to the high operating pressures necessary for maintaining the gas in a liquid state. Specifically, the cleaning vessel in a liquid carbon dioxide system operates at between 500-850 psi under ambient temperature conditions. The cleaning vessel, which typically has a relatively bulky heavy walled construction for withstanding the elevated pressures, is generally equipped with a main door which permits access to the interior of the cleaning vessel for the loading and unloading of garments or other items. In addition to the main door, various other doors, access panels, hatches and the like may be associated with the regular operation and maintenance of the dry-cleaning apparatus. For example, the dry-cleaning apparatus may be provided with doors to other areas of the system, such as filters and cleanout areas, which must be accessed on a regular basis for routine cleaning or maintenance and which also communicate with the high pressure atmosphere in the cleaning vessel or otherwise are exposed to elevated pressures.
While the size and weight of the main door on the cleaning vessel requires the provision of an automated opening and closing mechanism, the smaller doors which are used to access the filters and cleanout areas generally can be operated manually and may need to be opened as frequently as after the completion of each dry-cleaning load. As a result of the high operating pressure of the dry-cleaning system, extreme care must be taken to ensure that none of the doors which communicate with areas of the dry-cleaning system which are exposed to elevated pressures are opened when the system is pressurized or charged. As will be appreciated, the risk of a potentially dangerous and damaging discharge of the high pressure carbon dioxide in the system is particularly acute with doors that are manually opened on a regular basis. If one of these doors, hatches or the like is opened when the system is pressurized, the rapid discharge of high pressure carbon dioxide from the system could result in injuries to the operator and damage to the dry-cleaning machinery. Thus, in order to protect against an accidental discharge of the pressurized contents of the dry-cleaning system, safety lock-outs preferably should be provided, at least, on the manually operable doors of the cleaning vessel that are used most frequently.
Several different types of safety lock-out devices or mechanisms have been developed which prevent a pressure vessel door from opening when the vessel is charged. These lock-out devices, however, have several significant drawbacks. One drawback which is common to many lock-out devices is a reliance on an outside or external power source. For example, one known device utilizes air cylinders which are actuated by an electronic controller when the pressure vessel is charged to provide the safety lock out. Such devices, however, will not function properly when the external power source fails, possibly resulting in the door failing to be properly locked or in the door becoming stuck. The external location of the power source also makes it more vulnerable to damage and inadvertent shut-down. Additionally, the external power source could also be used to bypass the lock-out device.
Another significant problem with many lock-out devices is that they utilize relatively complex designs which are quite costly. In a highly competitive market such as the dry-cleaning industry, maintaining the costs of the dry-cleaning system as low as possible is extremely important. In these circumstances, dry-cleaning operators may be encouraged to forego costly safety features such as lock-out devices in order to minimize equipment costs. Thus, while maintaining cost requirements to a minimum is always an important object, it can be even more critical with dry-cleaning equipment. Moreover, the complex design of many lock-out devices makes them less reliable, and therefore prone to failure.
Other conventional lock-out or safety devices are manually operable, and thus often are less reliable and more susceptible to problems. For example, another known safety feature which guards against a rapid discharge of the pressurized contents of a pressure vessel resulting from the opening of a cover or door on the vessel, consists of a nut which must be drawn off in order to open the door or cover. As the nut is drawn off, the pressure is allowed to bleed out of the interior of the pressure vessel at a controlled rate. However, if the nut is drawn off too rapidly it can result in a potentially dangerous and damaging discharge of the pressure vessel contents.